1. Field of Invention
The present invention relates to a copper damascene process. More particularly, the present invention relates to a retardation layer for preventing copper diffusion and the fabrication method thereof, applicable to the fabrication method of a copper conducting wire.
2. Description of Related Art
In the conventional semiconductor device, a metal interconnect is made of aluminum or aluminum/copper alloy. It is known that copper has advantages, such as low resistance, high conductivity, low electron migration (EM), and so on, and is capable of being developed in the damascene process, so the future semiconductor process is developed in a direction where the metal interconnect is made of copper. As a result, the transmission speed of the device is increased, and the fabrication flow is simplified by applying the damascene process.
However, copper atoms may diffuse rather quickly in a silicon oxide layer, leading to a device failure or an inappropriate bridging between the metal interconnects. Although a conventional barrier layer (TiN/Ti or TaN/Ti) is used to retard the diffusion of copper atoms, such retardation effect is reduced by high temperature.
FIG. 1 is a schematic, cross-sectional diagram illustrating a conventional copper damascene manufactured with the barrier layer made of TiN/Ti. A part of the metal interconnect in the semiconductor device is shown in the diagram, wherein forming a tungsten plug 102 in a dielectric layer 100 provides an electrical coupling between an aluminum layer 104 and a device located below the tungsten plug 102. A copper conducting layer 106 is laid in an inter-metal dielectric (IMD) layer 108, while the barrier layer 110 made of TiN/Ti is formed between the IMD layer 108 and the copper conducting layer 106.
However, the barrier layer of the copper interconnect is usually made of TiN/Ti or TaN/Ti, as mentioned above, so it is limited in its ability to retard the diffusion of copper atoms. Under high temperature and long duration, the retarding effect may still be poor. Thus, this causes a device failure.